1. Field of the Invention
The present invention relates to a negative planographic printing plate precursor. More specifically, it relates to a planographic printing plate precursor capable of image formation by irradiation such as visible or infrared laser, and thermal image formation with ultraviolet lamps, thermal heads, and the like. The present invention also relates to a stack of the planographic printing plate precursors.
2. Description of the Related Art
Conventionally, a plate having a lipophilic photosensitive resin layer provided on a hydrophilic support has been used widely as a planographic printing plate precursor, and a desired printing plate is obtained by a plate-making method which usually involves masked light exposure (surface light exposure) via a lithographic film and then removing a non-image area by dissolution. In recent years, digitalization techniques which involve electronic processing, accumulation and output of image information with a computer are spreading. A wide variety of new image output systems compatible with these digitalization techniques have come to be used in practice. As a result, there has been demand for computer-to-plate (CTP) techniques for producing a printing plate directly by scanning a highly directional light such as a laser light according to digitalized image information without a lithographic film, and the provision of a planographic printing plate precursor adapted to these techniques has proved a significant technical challenge.
Examples of the proposed negative planographic printing plate precursors allowing such a scanning exposure include those having a photopolymerizable photosensitive layer containing a photopolymerization initiator, an addition polymerizable ethylenic unsaturated compound, and a binder polymer having a repeating unit of a particular structure soluble in alkaline developing solution, and as needed an oxygen blocking protective layer, formed on a hydrophilic substrate, (see, for example, Japanese patent application laid-open (JP-A) No. 2004-318053). Also proposed were negative planographic printing plate precursors having a photopolymerizable photosensitive layer and an oxygen blocking protective layer containing an added inorganic lamellar compound formed on a hydrophilic substrate, (see, for example, JP-A No. 11-38633).
There exists a need for further improvement in productivity in platemaking of such photopolymerizable negative planographic printing plate precursors. For example, shortening a time required for the exposure step leads to improvements in productivity. Normally, photopolymerizable planographic printing plate precursors are stored, transported, and converted into printing plates in a state in which they are stacked with interleaf sheets inserted between plate precursors. In platemaking with such stacks of planographic printing plate precursors, the interleaf sheets need to be removed in the exposure step, and the period of time needed for removing the interleaf sheets makes the exposure step more inefficient. To improve such inefficiency, it is possible to eliminate the step of removing the interleaf sheets by stacking the planographic printing plate precursors without inserting interleaf sheets.
The interleaf sheet has a function of preventing adhesion between planographic printing plate precursors, and preventing scratching due to abrasion between the photosensitive layer side surface of a planographic printing plate precursor and the support side back surface of the adjacent plate precursor. Thus, in conventional photopolymerizable planographic printing plate precursors, when stacked without inserting interleaf sheets therebetween, problems occurred that the planographic printing plate precursors adhered to each other, and the photosensitive layer side surface of the support was abraded and scratched with the rear surface of the adjacent planographic printing plate precursor, and so further improvement is demanded.
As described above, there has been a need for a planographic printing plate precursor, which even when plural planographic printing plate precursors are stacked with no interleaf sheets, is excellent in preventing adhesion between planographic printing plate precursors, and capable of suppressing occurrence of scratches caused by abrasion between a photosensitive layer side surface and a back surface of a support. However, such a planographic printing plate precursor has not yet been provided.